test(git): speed up the hunks test setup with a flush hook

lua/git/hunks.lua

@@ -399,6 +399,11 @@ end
 
 local schedule, sched_handle = util.keyed_debounce(recompute, 100)
 
+---@param buf integer
+function M._flush(buf)
+    sched_handle.flush(buf)
+end
+
 ---@param buf integer
 function M.attach(buf)
     if states[buf] then

test/git/hunks_test.lua

@@ -15,6 +15,7 @@ local function setup(committed, worktree, file)
     vim.cmd.edit(dir .. "/" .. file)
     local buf = vim.api.nvim_get_current_buf()
     hunks.attach(buf)
+    hunks._flush(buf)
     t.wait_for(function()
         local s = hunks.state(buf)
         return s ~= nil and s.index ~= nil
@@ -135,6 +136,7 @@ t.test("editing the buffer refreshes signs", function()
     t.eq(#state.hunks, 0)
     vim.api.nvim_buf_set_lines(buf, 1, 2, false, { "CHANGED" })
     vim.api.nvim_exec_autocmds("TextChanged", { buffer = buf })
+    hunks._flush(buf)
     t.wait_for(function()
         local s = assert(hunks.state(buf))
         return #s.hunks == 1